We bought an apartment from someone who build his sukkah on an adjoining mirpeset (actually at ground level as the apartment is built into the side of a mountain). A neighbour had wanted to build a path from the building one floor up over the mirpeset to an adjacent patch of land, but the previous owner refused permission.
On the day that we moved in, we found workers beginning to build a path above “our” mirpeset. When we challenged the neighbour, he told us that the mirpeset actually belongs to the building, and that he can do whatever he wants over it, or indeed in it. He explained that he hadn’t done so previously because he wanted to avoid an argument with the previous owner, but now that he’s gone, he isn’t going to wait any longer.
We have since determined that the mirpeset is indeed registered to the building in tabu. The previous owner claims that since the mirpeset is adjacent to his apartment, and he has a door opening to it, it is “accepted practice” that it should be considered his. (He was the exclusive user of the mirpeset for over 20 years, so presumably he could claim chazakah as well.)
Can the land actually be considered as belonging to the previous owner (and now us)? We would have preferred to reach a compromise, but the area for a sukah is small, and it’s difficult to limit it further.
The fact that your seller used the area for his Sukkah does not make it his or yours, even if he did so for many years. It is possible that he might achieve a Chazakah with regard to using the area for a Sukkah – but if there was an ongoing debate about the property, and the neighbors clearly wanted to use it for other purposes, this will also be far from clear.
However, I don’t see why he has the right to build a path onto the land. Does he have planning permission to do this? Why is his use of the land preferable to yours?
Under the circumstances, you should perhaps challenge him, politely but firmly, and ask why he has any right to the patch. If it belongs to the building, it is the joint property of all owners, and no single person can make changes and take action on the land.